This project is directed at characterizing the involvement of light stimulation in the loss of discs from the tip of photoreceptor outer segments. Using in vivo and in vitro preparations analyzed with light microscopy, electron microscopy, autoradiography and cytochemistry, it will determine the subcellular mechanism involved in loss of the outer segment tips. It will also evaluate the mechanism of transport of disc debris to the lysosomal system within the pigment epithelium.